: A man named Stuart Anderson suddenly collapses, revealing a gruesome infection on his leg while chanting the letters "BRT" .

The horror starts at a where several first responders are relaxing.

The story begins with a rare and terrifying (necrotizing fasciitis) that begins spreading rapidly across the city. The Outbreak Begins

: Shortly after, Ambulance 61 discovers two more victims dead from the same infection in a private residence.

: The original victim, Stuart Anderson, is identified as a lab assistant who had previously made threats via email, suggesting a bioterrorist plot. Personal Stakes and Danger

: Firehouse 51 responds to a major fire at Central Chicago University . While inside, Kelly Severide notices a laboratory wall bearing the same "BRT" initials the original victim mentioned.

: Investigations by the Office of Fire Investigation (OFI) confirm the university fire was deliberately set to destroy evidence in a lab that was actually researching treatments for this specific bacteria.

: Additional cases surface, including a woman and her child at a gas station, leading the CDC to step in as the situation escalates into a full-scale city epidemic. Investigation and Suspicion